Let's talk about what happens during the maneuver that brings tens, at times hundreds of pounds up in the air, against the laws of gravity.
Once on the runway, after completing the last checks of the onboard systems, and after having been cleared by the control tower, pilots increase the engines thrust all the way up to the appropriate takeoff power.
I said "appropriate", and not "max" power, because very rarely full power is needed for takeoff. The correct amount of thrust is computed for every single takeoff, and it depends on a lot of variables, such as the aircraft's weight, the runway length, the actual meteorological conditions, the presence of mountains and/or obstacles around the airport, and a few more. Calculations are carried out by pilots by using specific charts or a computerized software.
The resulting power to be used is such that the airplane will be able to either safely stop or get airborne using the whole runway length (without leaving any unused tiny bit), should an engine failure occur in the most critical phase of the takeoff run.
This is done in order to increase engines life and reduce fuel consumption.
In other words, the longer the runway, and the lighter the aircraft, the smaller is the amount of power needed for takeoff.
Once the takeoff roll has begun, while one of the pilots keeps a close eye on the engine instruments and makes sure that all is ok, the other pilot "drives", by maintaining directional control at the centre of the runway.
The takeoff roll is divided in different phases.
The first one, from the beginning to a certain speed (usually around 100 mph), is considered a "low energy phase"; should any anomaly occur during this phase, pilots are inclined to stop the takeoff. Speed is indeed very low, and interrupting the run does not imply any danger. Most of the times, after such an event, it is possible to quickly fix the problem and go back to the beginning of the runway to start all over again.
The second phase goes from the end of the first phase to a precise speed, called "V-one", and it is considered of "high energy"; during such phase, takeoff will be interrupted only for serious anomalies or events that could jeopardize safety should the airplane get airborne.
The reasons for deciding to stop in this phase are very few, the most common being a fire onboard, an engine failure, an unexpected obstacle on the runway.
But, as we said it is a high energy phase, in all "non critical" cases it is preferred to continue the takeoff because, although the remaining runway would allow the airplane to stop, the braking action would be rather intense, and could lead to unpleasant consequences (brakes overheat or fire, tyre bursts etc.)
V1 speed is very important, because it represents the limit beyond which the airplane is so fast that is not stoppable in the remaining runway, while it is fast enough to be able to keep accelerating and takeoff using the remaining runway, should an engine failure occur at any time after V1.
Because of this, after V1 pilots MUST get airborne, regardless of what happens on board.
No matter who is the pilot at the controls for the sector, it is always the Captain the one who is responsible for the decision to stop or continue the takeoff roll, and for this reason, he will keep his right hand on the engine throttles during takeoff, ready to intervene, up to V1 speed, after which he will move away his hand as a reminder that from that moment on the takeoff run has to be continued, no matter what.
Confused? Too complicated?
Stay calm... pilots constantly practice failures during takeoff in the simulator, keeping their skills up to speed and reviewing all the applicable procedures.
Let's go on...
Once beyond V1, usually around 150-200 mph, the next characteristic speed is "VR", at which the airplane can finally get airborne with the necessary energy to fly over all the obstacles along the takeoff path (again, even if an engine failure occurs at any time).
The pilot at the controls will pull the control yoke (or stick, depending on the aircraft model) in order to lift the nose gear from the runway and make the aircraft's "nose" point upwards, and a few seconds later, the main gear under the aircraft's belly will also detach from the ground.
We are airborne!!!
Well, the takeoff maneuver is not over yet...
when surely airborne, the gear will be retracted. As soon as a safe altitude is reached (usually 1000 ft.), engine power is reduced to the so called "climb thrust", as in order to make the aircraft climb, less than takeoff power is required.
So, don't freak out if, a few moments after takeoff, you feel like the engines are abruptly losing power... it is normal!
Lastly, there is an acceleration phase, in which the "flaps", that helped us sustaining the airplane in the air at low speed, get retracted, and the climb speed of 250-300 mph is reached.
Could you imagine soooo many things happened in a minute or two?
Don't Worry Fly Happy!
